Anaerobic biological wastewater treatment is one of the more common techniques in the treatment of wastewater that contains organic contaminants. An anaerobic sludge bed is the most commonly used reactor in anaerobic biological wastewater treatment. However, since anaerobic microorganisms have low yield, a key technical issue for an anaerobic sludge bed reactor is how to retain large quantities of anaerobic microorganisms in the reactor in order to optimize the performance of the anaerobic sludge bed reactor. At present, commercially available anaerobic sludge bed reactors include Biothane® UASB and BIOPAQ® UASB reactors. UASB is an abbreviation of “Upflow anaerobic sludge bed.” The applicant of the present invention has disclosed a UASB reactor in Taiwan Utility Patent No. 156653. One of the key techniques of a UASB reactor includes the design of a solid-gas-liquid three-phase separator.
The conventional design of a three-phase separator is limited by the size of the anaerobic sludge bed reactor, and by the properties of the microorganisms (e.g. the size and density of the microorganisms, etc.), which impose extremely high limitations on the hydraulic load of such a separator. For a conventional separator, the typical hydraulic load per unit area (front projection area) is generally 15-30 m3/m2-day. Therefore, when the concentration of the organic pollutants in the wastewater is low, the efficiency of the anaerobic sludge bed reactor per unit volume is restricted by the hydraulic conditions, and the reactor cannot perform desired functions.
A dissolved-air flotation (DAF) wastewater treatment technique is commonly used for wastewater treatment in a food processing plant, wherein air dissolved under high pressure is mixed with wastewater in a DAF tank to form numerous tiny bubbles that adhere onto solid particles in the wastewater (such as fat and protein particles that are generated during the washing of meat). Consequently, the air-buoyed solid particles that float on top of the wastewater in the DAF tank can be skimmed off, and the processed water can be discharged from the bottom or middle section of the DAF tank. A DAF tank is commercially available, and has been disclosed in various patents, such as U.S. Pat. Nos. 5,382,358, 5,538,631, 5,863,441, 6,174,434 and 6,599,418. U.S. Pat. No. 6,599,418 discloses a wastewater treatment device combining DAF with a gravitational sedimentation mechanism, wherein wastewater is first introduced into a gravitational sedimentation chamber located at a lower section of the device. Heavier solid particles precipitate first; the water containing lighter solid particles next goes through a serially connected flow channel and enters a DAF chamber located at a top section of the device to undergo an ordinary DAF treatment. An air dissolving device is mounted in the serially connected flow channel. The contents of U.S. Pat. No. 6,599,418 is incorporated herein by reference.
Those skilled in the art generally declare that anaerobic microorganisms should avoid contact with air in order to prevent reduction of the decomposing ability thereof of organic pollutants. Thus, to date no disclosure or suggestions are present in the prior art for solving the problems associated with the hydraulic load restrictions in an anaerobic microorganism treatment technique using a DAF wastewater treatment technique.